JPH0753976A - Oxidation of methane - Google Patents

Abstract

PURPOSE:To efficiently oxidize methane in a gas by using a product of coprecipitation of Co and Pd as a catalyst. CONSTITUTION:A solution containing an acetate, nitrate, oxalate, chloride or the like of Co is combined with a solution containing a nitrate, chloride, amine complex or the like of Pd in a Pd/Co atomic ratio of 0.001-1, and the solvent is removed from the combined solution, and the residue is dried and burnt to obtain a catalyst comprising a product of coprecipitation of Co and Pd. This catalyst is packed into a normal pressure fixed bed reactor, and a gas containing 0.001-10% methane and oxygen is passed through the reactor under conditions of a hourly space velocity of 100-500000hr<-1> and a temperature of 200-800 deg.C to oxidize the methane.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a catalyst and method for oxidizing methane in a gas.

[0002]

2. Description of the Related Art At present, methane is drawing attention as an inexpensive energy source and is widely used as a main component of fuel and city gas for power plants. Further, in order to reduce the amount of nitrogen oxides that cause air pollution, it is desired to develop a catalyst for methane oxidation using a catalyst.

On the other hand, since methane is a compound having an adiabatic effect equal to or higher than that of CO ₂ , its removal method is drawing attention from the viewpoint of global warming problem. Lakes, natural gas fields, flue gas, etc. can be raised as sources of methane released to the atmosphere. Among the combustion exhaust gas, the main component of hydrocarbons in the exhaust gas of city gas which has been widely used in recent years is methane, and its removal is desired. However, since methane has low oxidizability, it is not easy to oxidize and remove methane.

Under such circumstances, a catalyst in which a noble metal is supported on an oxide carrier such as alumina, for example, a catalyst in which palladium or platinum is supported on alumina is widely known as a catalyst for oxidizing methane.

On the other hand, a catalyst containing palladium is also known as an automobile exhaust gas catalyst called a three-way catalyst. In JP-A-4-215845, a coprecipitation product of cobalt and palladium is an automobile exhaust gas. Proposed as a purification catalyst. Although the catalyst is disclosed to have the ability to remove hydrocarbons at low temperatures, it is generally
Hydrocarbons in automobile exhaust gas are hydrocarbons mainly having olefins such as ethylene and propylene and having a high oxidizability and having 2 or more carbon atoms, and the oxidation activity of methane is not mentioned at all.

[0006]

As a catalyst for oxidizing methane, it is known that a noble metal is supported on an oxide carrier such as alumina as described above. However, under low temperature conditions, a low concentration of methane is oxidized. Insufficient to do so, and higher catalytic performance is required.

An object of the present invention is to provide a method for efficiently oxidizing methane in gas.

[0008]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that the use of a coprecipitation product of cobalt and palladium as a catalyst can efficiently oxidize methane in a gas. The present invention has been completed and the present invention has been completed.

That is, the present invention provides a method for oxidizing methane in a gas using a coprecipitation product of cobalt and palladium as a catalyst.

The present invention will be described in detail below.

In the present invention, the coprecipitation product of cobalt and palladium is obtained by obtaining a solid component composed of cobalt and palladium from a solution containing cobalt and palladium. The preparation method is not particularly limited,
Conventionally known methods, such as an evaporation dryness method, a coprecipitation method, a hydrolysis method, and a thermal decomposition method, can be mentioned. The composition ratio is not particularly limited, but 0.001 to 1 in terms of Pd / Co atomic ratio
If The cobalt source is not particularly limited, and acetate,
Examples thereof include nitrates, oxalates and chlorides.
The palladium source is not particularly limited, and examples thereof include nitrates, chlorides, ammine complexes and the like.

The coprecipitation product of cobalt and palladium may be subjected to a pretreatment such as drying or calcination before use as a catalyst.

The catalyst comprising the coprecipitation product of cobalt and palladium according to the present invention may have any shape, structure, etc., such as powder, pellets and honeycombs.

The methane oxidation catalyst of the present invention is formed into a predetermined shape by adding a binder such as alumina sol, silica sol or clay, or is made into a slurry by adding water, and alumina, magnesia, cordierite or the like in the shape of a honeycomb is formed. It may be used after being applied to the refractory base material.

The present invention is directed to a gas containing methane and oxygen. Methane concentration is not particularly limited, but 0.00
1% to 10% is preferable. It must also contain sufficient oxygen to oxidize methane. Examples of these gases include mixed gas of methane and air and city gas combustion exhaust gas. If oxygen is insufficient, oxygen may be added before adding the catalyst.

The space velocity, temperature, etc. when oxidizing methane are not particularly limited, but the space velocity is 100 to 500000 h.
It is preferable that the temperature is r ⁻¹ and the temperature is 200 to 800 ° C.

[0017]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Example 1 <Preparation of Catalyst 1> 1 liter of a mixed aqueous solution (Pd / Co = 0.01) consisting of 27 g of cobalt nitrate and 0.27 g of palladium nitrate was added.
50 ml of sodium carbonate at 0.5 ml / sec at room temperature
Was added dropwise to 2 liters of an aqueous solution in which was dissolved and stirred. After leaving this solution for 1 hour, it was filtered, washed and dried.
After that, it was calcined in an air stream at 350 ° C. for 3 hours to obtain a cobalt and palladium coprecipitation product, which was designated as catalyst 1.

As a result of elemental analysis, the atomic ratio of cobalt to palladium was 1: 100, and the weight ratio of palladium was 1.7 wt%.

Example 2 <Preparation of catalyst 2> 2 liters of an aqueous solution in which 50 g of sodium carbonate was dissolved,
A mixed aqueous solution (Pd / Pd / 27) containing 27 g of cobalt nitrate and 0.27 g of palladium nitrate at 0.5 ml / sec at room temperature.
Co = 0.01) was dripped into 1 liter and stirred. After leaving this solution for 1 hour, it was filtered, washed and dried.
After that, it was calcined in an air stream at 350 ° C. for 3 hours to obtain a cobalt and palladium coprecipitation product, which was designated as catalyst 2.

As a result of elemental analysis, the atomic ratio of cobalt and palladium was 1: 100, and the weight ratio was 1.7 wt% as palladium.

Comparative Example 1 <Preparation of Comparative Catalyst 1> In 90 ml of an aqueous solution in which 0.25 g of palladium nitrate was dissolved, silica (Fuji Davison Chemical Carreact 10) was used.
10 g of the resulting mixture was dried under reduced pressure at 80 ° C. to support palladium, and then dried at 110 ° C. for 20 hours to obtain Comparative Catalyst 1. As a result of elemental analysis, the weight ratio of palladium was 1.
It was 7 wt%.

Comparative Example 2 <Preparation of Comparative Catalyst 2> To 90 ml of an aqueous solution in which 0.25 g of palladium nitrate was dissolved, 10 g of alumina (Catalyst ACP-1) was placed and dried under reduced pressure at 80 ° C. to support palladium. rear,
It was dried at 110 ° C. for 20 hours to obtain Comparative Catalyst 2. As a result of elemental analysis, the weight ratio was 1.7 wt% as palladium.

Example 3 <Catalyst evaluation> Catalysts 1 and 2 and comparative catalysts 1 and 2 were crushed after tableting, respectively.
The particle size was adjusted to 12 to 20 mesh, and 2 cc of each was charged into the atmospheric fixed bed reactor. After pretreatment at 500 ° C. for 1 hour under air flow, the composition gas shown in Table 1 was changed to 50
The catalyst activity was measured at 300 ° C., 350 ° C., 400 ° C. and 500 ° C. by flowing at 0 ml / min.
Table 2 shows the purification rates of methane when the temperature reaches a steady state. The methane purification rate is the value obtained from the following equation, and is also the value obtained in accordance with it for other gases.

Methane purification rate (%) = (methane in−methane out) / methane in × 100 methane in: reaction tube inlet methane concentration methane out: reaction tube outlet methane concentration

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

From the results shown in Table 2, it can be seen that the use of the coprecipitation product of cobalt and palladium of the present invention as a catalyst makes it possible to efficiently oxidize methane in a gas even at a low temperature. Therefore, the present invention is a meaningful invention in terms of the global environment.

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Claims (1)

[Claims] 1. A method for oxidizing methane in a gas using a coprecipitation product of cobalt and palladium as a catalyst.